The term “hot tap” denotes establishment of a branching-point or a coupling point in a pipeline carrying fluid under pressure, without prior shutdown of the pipeline. A typical utilisation will be to connect a gas pipeline from a newly developed gas field to an existing gas pipeline, which results in significant savings compared to arranging a separate infrastructure for delivery of gas from the new gas field, particularly if the installations are located sub sea.
A hot tap operation represents no disadvantage for fluid-transport through the existing pipeline, as the operation is maintained all the time. By operation sub sea, ingress of water into the pipeline is avoided, as well as a subsequent costly pigging operation to remove the water. Likewise, corrosion problems caused by water, filling of an existing sub sea pipeline are avoided.
A number of arrangements exist for hot tapping, which have been used successfully over several years. So far the commercially available arrangements for sub sea hot tapping have required assistance from divers. There is a demand for hot tapping equipment for operation without assistance by divers, particularly for water depths deeper than 180 m, which is the maximal depth for planned diving operations in Norwegian waters.
An example of hot tap equipment is found in the Patent Application Publication US 2004/0089342 A1, where a method and an arrangement are described for friction stitch welding of a branch coupling to an existing pipeline. After the welding, openings are machined through the wall of the existing pipeline to complete the hot tap coupling. Seam stitch welding has a disadvantage of relatively low mechanical strength and utilisation of relatively complicated equipment. A demand exists for simplified equipment for hot tap operations.
Other examples of equipment for hot tap operations are described in the Patent Publications NO. 3144467, WO 00/60262, EP 235917, EP 304246 and EP 235917.